I'm sorry guys....RO water is out of the question for me. as it is quite expensive for me to install it. KH I have no idea.

What I did was I removed everything from the tank....like gravel plants ....only kept the stone which is connected to the oxygen, after two days the pH droped below 6.. so I just cannot understand whats goin wrong . there is nothin else in the tank that could effect the change. except a moss ball.